Spectrometers and other optoelectronic devices can be used, for example, to determine various characteristics or an object based on the wavelengths of light reflected by, transmitted through and/or absorbed by the object. Such devices may employ a broadband light emission source. In some cases, it is desirable for the broadband light source to be operable to emit light not only in the visible and mid infra-red (IR) parts of the spectrum, but also in the near IR part of the spectrum (e.g., 800-2500 nm). Some known techniques for providing such broadband light emission sources tend to be bulky, consume significant amounts of energy and/or are relatively costly.
Generally speaking, a layered stack including multiple layers (each with different band gaps) can be operable to emit light from each of the layers by injecting charge carriers into the stack via electrodes. The charge carriers (e.g., electrons) must make their way to each layer in order to combine with a complementary charge carrier (e.g., holes), wherein the electrons and holes emit light upon combination. As a result, a configuration that requires charge-carrier injection tends to impose a number of restrictions. For example, to enable charge-carrier injection, each layer in the stack must not exceed a certain thickness. This restriction on the thickness imposes, in turn, a restriction on the allowable composition of light emitted by such a layered stack. For example, the layers are often implemented as quantum wells, and the thickness of the quantum well dictates to a large degree the wavelength of light emitted by it. Thus, optimization of charge-carrier injection leads to restrictions on the wavelengths of light that can be emitted by a layered stack relying on charge-carrier injection. Further, in such a layered stack, each layer must be comprised of a material generally amenable to charge-carrier transport, which generally can be achieved via doping. Doping, however, tends to decrease the radiative-recombination efficiency. Further, electrical contacts (e.g., electrodes) must be made to such a layered stack.